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Lithium Batteries & What They Mean

Flywheel energy density is inevitably far below 5 percent that of gasoline. A full gasoline tank is over 80 percent gasoline by mass, and therefore can deliver more than 10 thermal kWh/kg. Carbon fibre going a mile a second -- it probably wouldn't really go that fast, for at that speed it would be too close to breaking stress. What if an insect hit the windshield? -- would hold 0.36 kWh/kg, but could never be 80 percent of the flywheel system mass. Four times less, maybe.

But its kinetic energy could be efficiently converted not only into a very sudden blast of friction heat if it broke and slid to a halt on the massive heat sink that would have to be there, but into propulsion energy. Maybe three times more efficiently than the gasoline's energy can be. That would take back some, which I approximate as all, of the factor of four lost to low mass fraction.

This very optimistic reckoning yields an estimate that a 100-kg flywheel system would yield 3.6 percent as many vehicle kilometres as a 100-kg gas tank. That is why, after the IEEE magazine article's optimism on flywheels, there has followed 13 years of nothing.

Lithium Batteries & What They Mean

Gene,

There was a lot of research done in flywheels throughout the late '90's. One particular effort that went out was Rosen motors, a company set up by Ben Rosen (CEO of Compac computers) and his brother Harold Rosen (father of the geo-stationary communications satellite and founder of the former Hughes Space and Communications Division). They went a long way with flywheels but ended up disolving the company when they ran out of money. My recollection is that they found that:

- this sort of flywheels has very high specific power(w/kg) but not particularly good specific energy (wH/kg). Ie, they are great for storing energy to provide a huge kick but they aren't good for storing energy for going long distances
- gyroscopic effect of a fast rotating object is very bad with flywheels in moving vehicles, particularly quickly accelerating ones like passenger cars. This required very sophisticated mounting schemes.
- the 'turn to dust' idea is a hard sell and my not be totally true, especially when one has to design the rotor to stand up to the gyroscopic effect
- the costs of building flywheels that are strong enough to spin fast enough are very high, with little room to improve
- I seem to recall that there were other issues as well.

I believe that these looked like a good thing but didn't quite fit the bill, especially when compared with things such as super-capacitors (for high specific power) and the new battery technologies that were coming online at the time such as NiMH and Li-ion.

Lithium Batteries & What They Mean

It is amazing how technology advances when there is desire from many sources.
Does the obsticle of "Thermal Runaway" still not exist and is a problem when Lithium batteries reach a temperature of 130C turning them into a ball of fire or worse an explosion?
Ni-MH batteries as far as I know, are the only battery that can be disposed of in your local landfill. Anyone?

Lithium Batteries & What They Mean

John,

Thermal runaway was solved by placing a control chip (~$0.01) on each Li-ion cell. Lots of things in will get uncomfortable if heated to 130C. If you are afraid of that, you should see what the gasoline you have in your hybrid can do under adverse conditions (like a little static discharge). We can, however, learn to handle these things safely.

Seriously though, there were some big problems with the 1st Li-ion batteries used in laptop computers (cell phones held off until the problems were solved) but these were solved using the control chips and to this date, with over 500million cellphones being sold each year, the only documented cases of meltdown were with cheap after-market batteries that were slipped in after the phones left the manufacturers.

I also don't know why you think Li batteries would be any more of a landfill problem than lead-acid ones - and mandatory recycling programs have essentially eliminated both the disposal problem with these as well as the lead supply problem.

Battery user:

Is it the battery manufacturers or the cellphone/computer manufactureres who are over-exagerating the lifetimes? With a 100:1 difference in power draw between cellphone modes and a 10:1 difference between computer operating modes, there is a lot of room for creative performance measurement or creating optimal conditions under which (conveniently) to measure.

Having been in both businesses, I can assure you that it is much easier to accurately verify the capacity of a battery than the power drawn by a computer or cellphone under 'normal' conditions.

Lithium Batteries & What They Mean

Lithium Batteries & What They Mean

Any and all ideas or practices that improve the world's energy situation are worth consideration. Often, differing energy improvement ideas are able to work well with each other. The Prius not only combined an electric motor with a gasoline engine but also incorporated advanced aerodynamics, low rolling resistance and various other methods into a single vehicle. It's good to focus on and put our effort into the best ideas but not to reject others because we found a good one.

The point of adding the link about the Earth Romer was to point to the energy efficiency of the unit and specifically to the photovoltaics on top. As stated in the literature, the builders of this vehicle leave its freezer stocked at all times. When they take it on a trip, it's ready to go. Even though it may have been parked for months. This is a neat trick and accomplished with the use of photovoltaics. No propane. No plugging into the grid. Just passively keeping the batteries hi and the freezer cold until they're ready to be used.

Batteries, capacitors, flywheels, hydraulic boosts, biofuels, photovoltaics, you name it, they all have a place. But for now, batteries look most likely to succeed (at least on the largest scale) and therefore probably deserve our continued scrutiny more than any other current option.

Lithium Batteries & What They Mean

Lithium batteries are clearly critical to getting off oil transport. There is no doubt that they offer a power / weight ratio far better than any other battery technology. I hypothesize that several aspects of them need to be in place to allow an effective price-competitive car to be manufactured:

- they apparently have issues in delivering sudden surges of power. Possibly supercapacitators can help here

- they are too expensive - we can only hope that better design and more R&D can resolve this. In this context if the US Government invested the same R&D into lithium as it has into hydrogen - well this would help.

- in the above context my understanding is that there are no fundamental reasons why lithium batteries should be expensive. Unlike Nickel-Hydride the patents are widely held so there should be the same issues as exist with the Cobalsys patents. The raw materials are plentiful and cheap

- I think we need to be thinking in terms of an electric car which has a small petrol generator which backs up the battery. Perhaps a 200cc motor which delivers say 20k/w. This shouldn't be too heavy

- finally I would suggest that the vehicle is modular. That is, it can battery packs as complete units. That way I could choose between keeping the price to an absolute minimum (one battery pack) or go for say 3 packs for rather more money and get rather more range. Likewise the generator could be a modular unit.

A truly interesting question would be what would be the price point of this vehicle?